Roger Penrose made his name with the Penrose-Hawking theorems and twistor theory. He is also well-known for writing books with very many pages, most recently “Fashion, Faith, and Fantasy in the New Physics of the Universe.”

One man’s noise is another man’s signal.

Penrose doesn’t like most of what’s currently in fashion, but believes that human consciousness can’t be explained by known physics and that the universe is cyclically reborn. This cyclic cosmology, so his recent claim, gives rise to correlations in the LIGO noise – just like what’s been observed.

The LIGO experiment consists of two interferometers in the USA, separated by about 3,000 km. A gravitational wave signal should pass through both detectors with a delay determined by the time it takes the gravitational wave to sweep from one US-coast to the other. This delay is typically of the order of 10ms, but its exact value depends on where the waves came from.

The correlation between the two LIGO detectors is one of the most important criteria used by the collaboration to tell noise from signal. The noise itself, however, isn’t entirely uncorrelated. Some sources of the correlations are known, but some are not. This is not unusual – understanding the detector is as much part of a new experiment as is the measurement itself. The LIGO collaboration, needless to say, thinks everything is under control and the correlations are adequately taken care of in their signal analysis.

A Danish group of researchers begs to differ. They recently published a criticism on the arXiv in which they complain that after subtracting the signal of the first gravitational wave event, correlations remain at the same time-delay as the signal. That clearly shouldn’t happen. First and foremost it would demonstrate a sloppy signal extraction by the LIGO collaboration.

Ian Harry did not respond to my requests for comment. Neither did Alessandra Buonanno from the LIGO collaboration, who was also acknowledged by the Danish group. David Shoemaker, the current LIGO spokesperson, let me know he has “full confidence” in the results, and also, the collaboration is working on a reply, which might however take several months to appear. In other words, go away, there’s nothing to see here.

Penrose’s cyclic cosmology works by gluing the big bang together with what we usually think of as the end of the universe – an infinite accelerated expansion into nothingness. Penrose conjectures that both phases – the beginning and the end – are conformally invariant, which means they possess a symmetry under a stretching of distance scales. Then he identifies the end of the universe with the beginning of a new one, creating a cycle that repeats indefinitely. In his theory, what we think of as inflation – the accelerated expansion in the early universe – becomes the final phase of acceleration in the cycle preceding our own.

Problem is, the universe as we presently see it is not conformally invariant. What screws up conformal invariance is that particles have masses, and these masses also set a scale. Hence, Penrose has to assume that eventually all particle masses fade away so that conformal invariance is restored.

There’s another problem. Since Penrose’s conformal cyclic cosmology has no inflation it also lacks a mechanism to create temperature fluctuations in the cosmic microwave background (CMB). Luckily, however, the theory also gives rise to a new scalar particle that couples only gravitationally. Penrose named it “erebon” after the ancient Greek God of Darkness, Erebos, that gives rise to new phenomenology.

The erebons have a mass of about 10-5 gram because “what else could it be,” and they have a lifetime determined by the cosmological constant, presumably also because what else could it be. (Aside: Note that these are naturalness arguments.) The erebons make up dark matter and their decay causes gravitational waves that seed the CMB temperature fluctuations.

Since erebons are created at the beginning of each cycle and decay away through it, they also create a gravitational wave background. Penrose then argues that a gravitational wave signal from a binary black hole merger – like the ones LIGO has observed – should be accompanied by noise-like signals from erebons that decayed at the same time in the same galaxy. Just that this noise-like contribution would be correlated with the same time-difference as the merger signal.

In his paper, Penrose does not analyze the details of his proposal. He merely writes:

“Clearly the proposal that I am putting forward here makes many testable predictions, and it should not be hard to disprove it if it is wrong.”

In my impression, this is a sketchy idea and I doubt it will work. I don’t have a major problem with inventing some particle to make up dark matter, but I have a hard time seeing how the decay of a Planck-mass particle can give rise to a signal comparable in strength to a black hole merger (or why several of them would add up exactly for a larger signal).

Even taking this at face value, the decay signals wouldn’t only come from one galaxy but from all galaxies, so the noise should be correlated all over and at pretty much all time-scales – not just at the 12ms as the Danish group has claimed. Worst of all, the dominant part of the signal would come from our own galaxy and why haven’t we seen this already?

In summary, one can’t blame Penrose for being fashionable. But I don’t think that erebons will be added to the list of LIGO’s discoveries.

"and who I was counting on" - strictly speaking, I think this should be "and whom I was counting on" or "and on whom I was counting" (my mother, who was an English teacher, was very strict on that sort of thing, although the meaning is clear, and the who-whom distinction is probably disappearing).

Thanks for another interesting post. I went back to Dr. Carroll's blog, hoping to see an update in response to the counter-claim that the error was on Dr. Harry's side, but found nothing new there, either in the original post, its comments, or a new post. I guess we must wait for the official LIGO response, but as things stand, "something is wrong on the Internet". (One way or the other.)

Professorin B, you could have added that in the far distant future all matter will end up in black holes, then spewed out as Hawking radiation, so matter-less conformal symmetry would be restored. I agree that erebon is pretty pathetic, but hey, even Dirac began to slip up in his 80s.

Nicely written and interesting topic. Typo: “from one US-cost” to “from one US-coast”. [the Gulf coast to Pacific northwest coast, well 230 miles from the coast.]

Sir Roger Penrose’s erebons must be decaying in the Platonic realm of mathematics, not 4-dimensional spacetime. I recommend investigating Cinnabons which are heavenly and account for some of my extra mass.

I've always liked Penrose, so let me act as his partisan for a moment.

B: >> Roger Penrose made his name with the Penrose-Hawking theorems and twistor theory. He is also well-known for writing books ...

also some decent work in pure math, mainly Penrose tiles

B: >> Penrose has to assume that eventually all particles decay so that conformal invariance is restored.

True, but he's always admitted, even highlighted, this issue. Unlike some stringy types we could mention

B: >> I have a hard time seeing how the decay of a Planck-mass particle can give rise to a signal comparable in strength to a black hole merger.

The signal results from an entire galaxy's worth of them

B: >> Even taking this at face value, the decay signals wouldn’t only come from one galaxy but from all galaxies, so the noise should be correlated all over and at pretty much all time-scales – not just at the 12ms as the Danish group has claimed. Worst of all, the dominant part of the signal would come from our own galaxy and why haven’t we seen this already?

But he covers this objection in the cited paper:

"Of course, in this description, the black-hole encounter is almost irrelevant, serving merely to locate an individual galaxy in the sky. To test this, one need merely settle on some prominent galaxy—say the Andromeda galaxy—and look for correlations in the noise that has a time delay between the two detectors that corresponds to sources in the direction of that particular galaxy. The black-hole encounter would be completely unnecessary for this, and one does not have to wait for such occurrences in order to test the proposal. Of course, the dark-matter distribution in our own galaxy would be a major contributor, in this proposed scheme, and thus should be a major contributor to the signals referred to here. Clearly the proposal that I am putting forward here makes many testable predictions, and it should not be hard to disprove it if it is wrong."

It's far-fetched. But isn't it great that it can be tested, and falsified - using just the data from LIGO? Probably that will be done soon, CCC/erebon will fail, and disappear. That's what happens to most falsifiable scientific hypotheses.

It may be the fantasy of an old man whose family should have taken away the car keys, and the arxiv access, a while ago. Just the same it's real science, as opposed to (for instance) string theory, which only gets more popular when its predictions fail!

Thanks very much, B, for being open-minded, giving ideas you don't really like a fair hearing, we need more like you.

There are of course vacuum-correlations but they are (ususally) far too weak to be measurable. Craig Hogan claims that because of Holography they might be measurable, but his argument is, if anything, even sketchier than erebons.

Isn't it sort of obvious that if the "best-fit theoretical templates" are not exactly right then there will be correlations in the residuals? You could test this by using worse theoretical templates and checking if you get stronger correlations.

Yes, basically. If you take a theoretical (pre-calculated) template you'll almost always miss part of the signal. However, my understanding is that LIGO also does a non-templated search from which there shouldn't be correlations left pretty much by definition.

In the paper, Penrose says "…but the view here is taken (in opposition to that of “many-worlds” proponents) that since unitarity is already violated in quantum measurement, then it is not a universal truth;…"

I thought unitarity was a property of the matrices of probability amplitudes of evolution operators, and measurement is a separate thing (that is also inherently non-linear).

"human consciousness can’t be explained by known physics" Build a silicon neural net, train it. The result is immune to discretization. Statistically weak observations mathematize to miserable conclusions, then new particles beg detection. Theory and experiment publish to no empirical end. Galileo and Popper say, "First testable, then believable."

No doubt I'm misunderstanding something(s) but here's what I guess Penrose and collaborator(s) think.

LIGO data is very noisy. Correlations are very hard to find. LIGO's mind-set is that GW events are very rare: noise can't be coming from galaxies, but from equipment and random sources. They're simply not checking for any time-correlated (between Hanford and Livingston) noise. Conclusion reinforced by fact they didn't notice the correlations reported by Danes. Plus, at first Ian Harry had mistakes, so appears the whole idea was new to him, and to LIGO analysts. BTW note he's using Python! C++ would be expected, maybe others, not a script language, for high speed data processing. Anyway, apparently it simply never occurred to them that the noise might be correlated at 12 ms or any other time. If they didn't explicitly look they certainly wouldn't find given the vast amount of filtering and templating needed to get any sort of signal at all.

So Penrose recommends looking for correlated noise similar to Dane's findings, coming from any galaxy in the sky, regardless of merger events. As you say "the noise should be correlated all over and at pretty much all time-scales" but we should see a relation to nearby galaxies where it's stronger. Try Andromeda first. If found, then it's not "meaningless" noise. Rather it's a real physical phenomenon.

As for our own galaxy's "erebon decay" you ask "why haven’t we seen this already?" Per Penrose hypothesis, we have. Just look at the raw data - plenty of spikes. We might be able to pick out strongest spikes and analyze them as Milky Way events. Assuming erebons, with identical-size impulse events, identify same-size within short ms window, which gives some idea of direction, strength tells you the range, map to local DM. If it succeeds score one for Penrose!

Dane's analysis might already give a hint whether noise comes from identical-size impulses, but unlikely to see that at such distance. (I guess.)

"Correlated noise" from galaxies could exist, without Penrose being right. If it does LIGO people are currently realizing it. (BTW if they were using C++ or assembler they'd be realizing it sooner.) But the scary question is, with all that (putative real physics) going on, not being checked for, how often will it accidentally add up to spurious signal that fits the BBH merger template? About, maybe, 4 times since operation began?

I am not suprised to see correlated noise in the residuals of the two detectors at the same time shift seen for the observation itself.

Is it really beyond possibility that the fitted "template" does not exactly reproduce reality ? If it does not match the exact merger GW, then obviously one doesnt fully subtract the GW signal and the "residuals" will remain correlated.

"Just that this noise-like contribution would be correlated with the same time-difference as the merger signal."

And yet, LIGO did not see any of such signal: https://journals.aps.org/.../10.1103/PhysRevLett.118.121101

@George you should be careful before asserting things that the LSC does or does not: "They're simply not checking for any time-correlated (between Hanford and Livingston) noise."

Obviously, you haven't followed the literature enough... Check the paper above: "In this Letter, we report on the search for an isotropic background using data from Advanced LIGO’s first observing run O1. We search for the background by cross-correlating data streams from the two separate LIGO detectors and looking for a coherent signal. We find no evidence for the background and place the best upper limits to date on the energy density of the background in the LIGO frequency band. We also update the implications for a BBH background using all the data from O1."

" BTW note he's using Python! C++ would be expected, maybe others, not a script language, for high speed data processing."

I think Dr. Harry used Python for the examples he posted on Dr. Carroll's blog so that readers could follow his method more easily and reproduce his results if they wanted to - not because that is how LIGO signals are actually analyzed. At least, that is a more charitable assumption.

As I said before, with all the assumptions and charges being made, I would appreciate an update to Dr. Harry's post - but maybe the LIGO team have decided they need to spend time preparing an official response rather than informal blog posts. Still, an update could say just that.

I read Penrose's paper when you first tweeted about it, but was deeply disappointed with his non-explanation of the 12 ms delay in the correlations. At the end of your post you mentioned this as a problem, but I think it's a *big* problem! Noise is expected for lots of reasons, but correlated noise is not. Penrose's erebons offer noise but not correlated noise AFAICT. His effort to explain a correlation was so wrong that I suddenly lost a lot of respect for him as a scientist.

I was wondering if I was understanding this correctly myself, and I was really looking forward to any & all analysis of this paper. If black hole mergers create tons of erebons, then I'm completely mistaken about this flaw. But Penrose says "the black-hole encounter is almost irrelevant, serving merely to locate an individual galaxy in the sky." Either this is nuts, or I am. Those mergers all happened in *very* distant galaxies.

You're right. My statement "They're simply not checking for any time-correlated (between Hanford and Livingston) noise" is, taken at face value, stupid. Of course they're looking at it - somewhat. The paper you cite is not the best example, since they were already aware of Jackson et al's criticisms by 24 March 2017. But I remember seeing a LIGO study from roughly a year ago looking for such correlations - or similar - which unfortunately I can't track down at the moment. The statement should end with "... as carefully (thoroughly, seriously) as perhaps they should".

Please note my first sentence, which is very important: "... here's what I guess Penrose and collaborator(s) think." NOT, "here's what I think." If you backtrack to the beginning of this exchange with Sabine, you'll see this is about Dr. Penrose's paper - the blogpost topic. She asked how the quote from him, which I gave above, "covered" her objection. I believe this is more or less how he'd answer. But I don't know enough about CCC, erebons (?!), or LIGO, to defend his view against experts. Please ask him for further elucidation.

@JimV,

looks like you may be right also. Note, I wasn't going by Dr. Harry's guest blog. A year ago I was annoyed that almost all their public support is in Python. Didn't want to translate all those algo's; could have grabbed a Python interpreter off the net but never got around to it. However, digging deeper in response to your comment, it turns out Python may be only their public face. See https://wiki.ligo.org/DASWG/LALSuite. Evidently for their own work, they use C, which gives an even better impression of serious data-crunching competence than C++. Thanks for prompting me to find that!

Dr. Rush, thanks very much for your reply, and for the interesting facts and opinions you have posted (as I should have noted in my previous comment).

I am impressed by your scientific dedication to the truth. In that spirit, I will acknowledge that it didn't occur to me to try to Google how the LIGO team crunches their numbers until well after I submitted my earlier comment.

There's one catch: I'm afraid he might think you can point LIGO like a telescope!? Hard to believe he'd make such a mistake. But to start, let's pretend you can; makes it easier to explain his paper. I'll come back to the issue later.

DM is composed of erebons. (According to Penrose, not me! I'll omit that caveat from now on.) Erebons are constantly decaying, randomly. Each decay emits a GW "pop". It's such high frequency (10^43) that it's basically an impulse. If it were visible light, say, cyan, Then DM would be that color. DM, of course, surrounds galaxies. So every galaxy would be surrounded by a cyan halo. Andromeda would look prettier to the naked eye, bigger, and fuzzier. And our local Milky Way environment would have a very faint cyan tint everywhere.

LIGO is tuned to detect much lower frequencies, like 10^2, so you might think it wouldn't see erebons decaying at all. But Penrose argues that it will. Let's just accept that.

So - if we could point LIGO like a telescope - DM would appear as a halo around any galaxy, like the cyan mentioned above. When LIGO looks at the galaxy where the BBH merger occurs, it's also seeing a "haze" of erebon decay. They think it's just noise. And indeed it is, because it makes it harder to see the event we're interested in. But it's physically significant noise.

To check out the hypothesis, he recommends pointing LIGO at Andromeda (for starters) to look for this erebon-decay noise / haze.

So far, so good, I hope. Now let's get back to the truth: LIGO is not like a telescope. It's a fixed installation which, at any given time, is detecting GWs from a very large, 4-lobed (I think) region of sky. Crude "pointing" is achieved by time-correlating the Hanford and Livingston signals. Thus if they're hit at the same time, the signal is coming, roughly, from a huge cross-shaped region orthogonal to a line drawn between the two detectors. At H-L = 6.7 ms (for instance), the angle is something like 50 degrees (doesn't matter exactly).

When they find a BBH merger signal at a given correlation, they're concentrating on the region containing the host galaxy's DM, plus a lot more DM throughout the universe which happens to be at that angle (or, time delay). There's erebon decay everywhere, making noise they get rid of. That's why the rejected noise winds up with correlations that the Danish researchers found. BTW since they don't realize it's a real correlated physical signal, their data cleaning isn't maximal.

That's Dr. Penrose's view (not mine!). If you could point LIGO like a telescope, his paper makes more sense.

In previous post I sketched how to examine our galaxy. To examine Andromeda, wait until Earth's motion brings Andromeda into the quadrupole (I think) "antenna pattern". Then, at the appropriate angle, notice particularly strong "noise". Continue observing this excess signal, tracking Andromeda (her angle / time-delay, that is) across the sky. Ought to work. But applying this to any more distant DM concentration, like Virgo cluster, is dubious. Penrose doesn't seem aware of this difficulty. If so it does NOT invalidate his main ideas, but it is embarrassing.

@George Rush: I took Penrose's argument to be that the erebon decay related noise would be occurring everywhere so that inevitably it would be present "near" the source of a detected gravitation wave and therefore present in the filtered gravitation wave signal.

I don't see why the erebon decay signal would be seen with the BBH merger but not be seen in the background isotropy/anisotropy searches performed by Advanced LIGO.

Also would LIGO even be sensitive to such a high frequency (even accounting for redshift of the GW). The only LIGO strain graphs I found are limited to frequencies less than 10^3 Hz.

@Michael Musson, the word "near" needs unpacking - as you recognize, since you put it in "scare quotes". He's thinking the erebon-decay noise must be physically "near", namely, in the galaxy hosting the BBH merger event:

Penrose >> ... the “noise” which comes from the erebon decay from [b]that particular galaxy[/b] would indeed be correlated with the same time delay between the two detectors as would the signal from the black-hole encounter event. Of course, in this description, the black-hole encounter is almost irrelevant, serving merely to [b]locate an individual galaxy[/b] in the sky.

But in fact the correlated noise would come from all DM within the scope of LIGO observation. This huge region contains not only the host but maybe 10^5 or 6 more galaxies. We might say all this region is "near" the merger event, in a way. Although I have the greatest respect for Dr. Penrose, he seems not to understand this. (Even Newton made mistakes.)

In the CCC / erebon model, "the erebon decay signal would be seen with the BBH merger" and it would also "be seen in the background isotropy/anisotropy searches performed by Advanced LIGO". Probably someone already knows whether it's there or not - but perhaps the data analysis is more difficult than it appears. Anyway, it's not very likely that the correlated noise really is unrelated to the merger event, but it is an exciting possibility.

The situation is similar to Penzias & Wilson's discovery of CMB. As we all know, when they did the first effective observation of microwave frequencies, they expected only rare events. Instead they found "noise" coming from everywhere. It took a while to believe it was physical. Indeed, I remember a couple years ago LIGO did find an unexpected amount of ubiquitous noise, the source of which hadn't been tracked down when I saw the analysis. Maybe, unlike P & W, they just decided to live with it, and the truth is only now coming out.

LIGO definitely is NOT sensitive to high frequency GWs, as such. They can't even dream of tracking oscillations at 10^43 hz. The cutoff, as you say, is around 10^3. But Penrose argues it will be detected as an impulse, rather like a solid "particle" of gravitational disturbance. He ought to know: this is not really about LIGO, but GR.

Bottom line: wait a few days or weeks, answers will emerge. One could also download LIGO algo's and data, do the analysis oneself. But that would be a lot of trouble.

@JimV, thanks! But no "Dr", please. I never got the darn dissertation done. Excuse: I was getting an offer a day to do software, salary comparable to a full professor. But I have to admit: the work got a whole lot more difficult beyond Master's level. Programming, Mathematical Analysis, and finally Technical Directing on large U. S. Navy Submarine projects (what I wound up doing), was much easier.

@George Rush: Sorry I'm very late responding, probably too late. It does help me understand this paper more if I allow the false assumption that LIGO is directional. I had to re-read section 2 with that in mind, and it suddenly made a lot more sense. Thanks!

But because LIGO is not "pointed" anywhere at a given time, erebon decays can be ruled out as a source of the correlated noise in LIGO.

I believe that the time lag of the correlated noise matched the time lag of the signal for all three merger candidates. Time lags were 7, 1, and -3 ms for each candidate observation. If I'm reading the Creswell et al paper right, noise (after subtracting a theoretical signal) appears to have the *same* time lag as the signal in each of the 3 cases: 7, 1, and -3 ms. They also see correlated noise in a calibration signal. I'm not yet clear on what the time lag of that one is.

So even if nearby erebons were clustered in one part of the sky (and I think this is probably not true*), this would still fail to explain the LIGO noise mystery because it does not couple the time lag with the individual black hole merger signals.

* Nearby dark matter would be a large halo around Our Galaxy, as measured by rotation curves. This is assuming particle dark matter, and erebons *are* particle dark matter candidates. Distant dark matter would not be directional, and would be even less likely to look like noise at the frequencies LIGO is sensitive to.

@Topher, yes, the Creswell paper invalidates the erebon story. I should have read it before. My purpose was just to explain Penrose's paper, right or wrong. Penrose clearly thinks correlated noise could be found at all time delays. Since he must have read the paper, I assumed it couldn't say what it does, in fact, say.

Your previous comment was good "If black hole mergers create tons of erebons, then I'm completely mistaken about this flaw." But that's not Penrose's story. Maybe his next proposal will go with that idea!

I was willing to give him a partial pass on LIGO "pointing", but Creswell paper is ref. 1 in his proposal, so this comment makes sense also: "His effort to explain a correlation was so wrong ..."

@JimV's comment above is the appropriate conclusion: "I would appreciate an update to Dr. Harry's post ..." from LIGO. It does seem that (as Ricky Ricardo used to tell Lucy, for those of us who go back that far) "You've got some 'splainin' to do!"